1. Field of the Invention
The present invention relates to a system mounted on an automotive vehicle for detecting an obstacle such as a preceding vehicle by emitting radar beams and receiving beams reflected by the obstacle.
2. Description of Related Art
An example of an obstacle detecting system mounted on an automotive vehicle is shown in JP-A-2002-40137. In this system, radar beams such as light beams or millimeter-wave beams are emitted toward an obstacle such as a preceding vehicle, and beams reflected by the obstacle are received. Based on the reflected beams received by the system, a distance from the vehicle carrying the system to the preceding vehicle is detected. For example, if the distance between two vehicles becomes too short, a warning is given to a driver of the vehicle carrying the system, or the distance between two vehicles are maintained not to become shorter than a predetermine distance by controlling a traveling speed of the vehicle.
Laser beams are emitted while scanning in both the horizontal and vertical directions, thereby detecting an obstacle such as a preceding vehicle located in a predetermined scanning area. The distance to the preceding vehicle and its angular direction relative to a direction in which the vehicle carrying the system is traveling are detected based on the laser beams reflected by the preceding vehicle. In other words, the preceding vehicle is detected as plural dots reflecting the laser beams. The horizontal width and the vertical height of the obstacle such as a preceding vehicle are detected based on the horizontal angle of reflected beams and the vertical angle of the reflected beams, respectively.
More particularly, after one scan in the horizontal direction is completed, the vertical angle of the beam is changed by a certain angle and the next horizontal scan is carried out. This process is repeated until all the scanning area is covered. After one horizontal scan is completed, the plural dots reflecting the laser beams, which fall within a certain distance range from the vehicle carrying the obstacle-detecting system and within a certain width range in the horizontal direction, are grouped into presegment data. Further, the presegment data obtained by scanning each horizontal scanning line, which are close to one another, are grouped into main segment data. The presegment data and the main segment data include only a limited number of the reflecting dots detected in the scanned area to save a memory capacity in a RAM and to shorten data processing time.
When the vehicle is traveling on a curved road, a preceding vehicle is not detected in the center of the horizontal scanning range, but it will be detected at a fringe of the horizontal scanning range. To cope with this situation, a reference angular direction from which the grouping operation to form the presegment data is initiated is calculated based on a radius of the curved road. The reference angular direction extends to a point on the curved road where the preceding vehicle is most probably located. Thus, the presegment data are formed from the reflecting dots located close to the reference angular direction.
In the system disclosed in JP-A-2002-40137, the reference angular direction is calculated based on only the radius of the curved road. It is difficult, however, to assume the position on the curved road where the preceding vehicle is most probably located based on only the radius of the curved road. When the preceding vehicle is traveling on the curved road having a given radius, it will be most probably detected at a position closer to the fringe of the scanning angular range if the distance between two vehicles is large. On the contrary, if the distance is not large, the preceding vehicle will be detected at a position closer to the center of the scanning range even when the preceding vehicle is traveling on the curved road having the same radius. The distance between the vehicles is also important to correctly assume the position of the preceding vehicle in addition to the radius of the road. Therefore, it has been a problem in the system disclosed in JP-A-2002-40137 that the presegment data representing the preceding vehicle cannot be satisfactorily formed.